This application is based on Japanese Patent Application Laying-open No. 11-326805 (1999) filed Nov. 17, 1999 in Japan, the content of which is incorporated here into by reference.
1. Field of the Invention
The present invention relates to an electrophotographic photoconductor used for electrophotographic printers, copiers, and the like, more specifically to a single layer type positive charging organic photoconductor for electrophotography, which provides a good image quality even in repeated uses.
2. Description of the Related Art
Heretofore, as a photosensitive substance for electrophotographic photoconductor(hereinafter referred to as xe2x80x9cphotoconductorxe2x80x9d), an inorganic photoconductor having a photosensitive layer comprising an inorganic photoconductive substance such as selenium, selenium alloy, zinc oxide, cadmium sulfide has been widely used as a main ingredient. However, recently, intensive research and development has been conducted for electrophotographic photoconductor using various organic photoconductive substances as materials for photosensitive layer which has been applied in practical applications in view of low production cost and prevention of industrial and environmental pollution.
Recently, in order to satisfy such performances as sensitivity and durability, as the photosensitive layer, a function separation lamination type photoconductor comprising a charge generation layer containing a charge generation substance and a charge transport layer containing a charge transport substance is in the mainstream. Above all, various kinds of lamination type organic photoconductors have been proposed. Each of them comprises a charge generation layer and a charge transport layer. The charge generation layer includes a charge generation substance made of resin with a deposited or dispersed organic pigment, and also the charge transport layer includes a charge transport substance made of a resin with a dispersed organic compound of low-molecular weight. In the organic photoconductors numerous substances having good positive hole transportabilities are known as charge transport substance. However, substances having a excellent abilities of transferring electrons(i.e., good electron transportabilities) are very few.
Therefore, the lamination type organic photoconductor described above is often prepared as a negatively charged one, in which an electron transport layer containing a positive hole transport substance is laminated on the charge generation layer. However, the negative charging lamination type organic photoconductor has disadvantages in that a specific system is required for uniform charging and a large amount of ozone is generated which deteriorates the environmental condition.
With the aim of improving the above problems, various positive charging organic photoconductors are proposed. However, as described above, in the case of the negative charging type, a substance having a good positive hole transportability can be used as the charge transport substance, whereas in the case of the positive charging type, substance having good electron transportability is very few. Further, even a substance with a relatively good electron transportability often has a toxicity or a carcinogenicity, therefore the use thereof has been difficult.
In addition, recently, several electron transport substances which introduced a solubilizing group into the electron acceptable structure are proposed. For example, those substances are described in Japanese Patent Application Laid-open Nos. 1-206349 (1989), 3-290666 (1991), 4-360148 (1992), 5-92936 (1993), 5-279582 (1993), 7-179775 (1995), 9-151157 (1997), and 10-73937 (1998). Furthermore, for example, those substance are described in Bulletin of the Society of Electrophotography vol. 30, No. 3, p266-273 and p274-281 (1991), xe2x80x9cJapan Hard Copy ""92xe2x80x9dProceedings, Jul. 6, 7, 8, 1992 JA Hall (Otemachi, Tokyo) p173-176, xe2x80x9cJapan Hard Copy ""97xe2x80x9d Proceedings, July 9, 10, 11, JA Hall (Otemachi, Tokyo) p21-24, and xe2x80x9cPan-Pacific Imaging Conference/Japan Hard Copy ""98xe2x80x9d Preprints Jul. 15-17, 1998, JA HALL, Tokyo Japan p207-210. However, any of the compounds disclosed in the above documents is insufficient in its sensitivity and electrical characteristics when it is used in combination with the existing charge generation substance, thus there are problems in practical applications.
A lamination type organic photoconductor being positively charged has functionally separated layers (i.e., charge generation and charge transport layers). In this case, the charge transport layer is provided on a conductive substrate and contains an electron transport substance and the charge transport layer is provided on the surface of the charge transport layer and contains a charge transport substance. Further, a surface protection layer is necessary for the protection of the charge generation layer provided as a thin film. However, such a surface protection layer has the problems of the difficulty in its design and the need for being formed as a multilayer coating, resulting in increased cost. For solving such problems, furthermore, the photocoductor may be configured in a single layer type in which both the charge generation and transport substances are dispersed in a single film or in another type where a charge transport layer is further provided as the underlayer of such a configuration.
However, such a positive charging organic photoconductor does not always satisfy requirements for a photoconductor. In particular, one characteristic required to be improved is the control of the amount of toner deposited on the surface of the photoconductor. When toner is deposited in excess on the surface of the photoconductor, frequent maintenance becomes necessary because the toner consumption amount is increased. Further, the toner deposited in excess on the surface of the photoconductor tends to be a cause of print defect such as dirty background (toner deposition on a part which must be white in printing).
To improve such a disadvantage, in general, charging characteristics of the photoconductor are often controlled, and a change in composition of the photoconductor is essential for controlling the electrostatic characteristics. However, compositional change of the photoconductor is highly possible to generate a malfunction in association with the compositional change, requiring further changes in various photosensitive processes, which has problems of decreasing he development efficiency.
In view of solving the above problems, an object of the present invention is to provide a superior positive charging organic photoconductor having no print defects such as dirty background by considering the binder structure so as to be capable of reducing toner deposition amount to the surface of a single layer type positive charging photoconductor and the composition for reducing the toner consumption.
The inventors have conducted intensive studies for solving the above problems, found that the above object can be attained by using a polycarbonate resin containing polydialkylsiloxane having a specific repeating unit as a binder of a single layer type positive charging photoconductor and by containing a specific type of charge generation substance, and thus accomplished the present invention.
Specifically, the photoconductor of the present invention is an electrophotographic photoconductor comprising at least a photosensitive layer on a conductive substrate, wherein the photosensitive layer is a single layer type photosensitive layer containing at least a charge generation substance, a positive hole transport substance, an electron transport substance and a binder, wherein the binder contains a polycarbonate resin containing polydialkylsiloxane having a repeating unit represented by following formula (1): 
(wherein, R is alkyl group having 1 to 6 carbon atoms which may be the same as or different from each other, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 12 carbon atoms, B is (CH2)x, x is an integer from 2 to 6, n is an integer from 0 to 200, and m is an integer from 1 to 50), and the charge generation substance contains a phthalocyanine pigment. The electron transport substance is an acceptor compound.
In the present invention, the content of the polycarbonate resin is preferably 20 to 80 weight % of the total binder component, and the phthalocyanine pigment is preferably X-type nonmetallic phthalocyanine. Further, the positive hole transport substance preferably contains a compound represented by formula (2): 
and the electron transport substance preferably contains a compound represented by formula (3): 
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of the embodiments thereof taken in conjunction with the accompanying drawings.